Various types of optical viewing devices, such as video magnifiers, bar code readers, CMOS cameras, microscopes, and the like, require an illumination source to illuminate the object plane to be viewed. Typically the illumination source includes one or more point light sources (e.g. LEDs) that are arranged to impinge light directly on the object plane. Alternatively, the LEDs are directed against a mirrored surface, which in turn re-directs the light against the object plane.
One problem with the direct illumination system described above is that the illumination source shines directly on the object plane to be viewed. This results in certain areas of the imaged field of view appearing brighter than other areas due to direct reflection of the light source back into the imager, especially when the object plane is reflective (e.g., glossy-surface paper). Uniform brightness across the entire field of view would provide easier viewing of the object plane.
One problem with the indirect/mirrored illumination system described above is that an image of the LEDs and/or the imager itself often is reflected back into the imager when viewing a reflective object place. This in turn detracts from the viewing quality of the object plane.
Yet another problem with known illumination assemblies in general is that the illumination source is typically made up of LEDS, which often are either green or red. While such colored LEDs work well when imaging standard black-on-white objects, they present major problems when used with colored objects. For example, red-printed text cannot be imaged successfully using red LEDs as the illumination source. This same problem occurs with green text and green LEDs.